1. Field of the Invention
This invention relates to an environmental noise level estimation apparatus, a communication apparatus including the same, a data terminal apparatus including the same and a method of estimating an environmental noise level.
2. Description of the Prior Art
An environmental noise level estimation apparatus is known. Japanese patent application provisional publication No. 9-247247 discloses a voice communication equipment. FIG. 8 is a block diagram of this prior art voice compunction apparatus. FIG. 9 is a time chart of the prior art. A microphone 201 receives sound and generates a sound signal which is a/d-converted by an a/d converter 202. The a/d converted sound signal is coded by a coder 203 and modulated by a modulation circuit 204 to transmit the sound signal. A reception signal is demodulated by a demodulator 207 and decoded by a decoder 208. A volume of the decoded signal is controlled by a volume control circuit 209 in accordance with a calculated noise level. An output of the volume control circuit 209 is supplied to a speaker through a d/a converter 210. The output of the a/d converter 202 is also supplied to a noise level calculation circuit 205 to calculate the noise level. A noise level renewing circuit 206 renews the noise level in accordance with an output of the noise level calculation circuit 205.
In this equipment, an amplification level of a voice signal is detected, means values are detected, and a minimum means value is detected from a plurality of means values as a sound noise level by the noise level calculation circuit 205. The mean value is detected every interval t1 and the noise level is renewed every interval t2 including the intervals t1. The volume is controlled in accordance with the noise level by a volume control circuit 209 every interval t2. The noise level is renewed every plurality of intervals for obtaining a plurality of means values.